AMD Am188TMER, Am186TMER user manual Chip Select Unit

CHAPTER

5 CHIP SELECT UNIT

5.1OVERVIEW

The Am186ER and Am188ER microcontrollers contain logic that provides programmable chip select generation for both memories and peripherals. In addition, the logic can be programmed to provide ready or wait-state generation and latched address bits A1 and A2. The chip select lines are active for all memory and I/O cycles in their programmed areas, whether they are generated by the CPU or by the integrated DMA unit.

The Am186ER and Am188ER microcontrollers provide six chip select outputs for use with external memory devices and six more for use with peripherals in either memory space or I/O space. The six memory chip selects can be used to address three memory ranges.

Each peripheral chip select addresses a 256-byte block offset from a programmable base address (see section 4.1.1 on page 4-4).

The Am186ER and Am188ER microcontrollers also provide 32-Kbyte of internal memory, described in Chapter 6. The Internal Memory Chip Select Register is described on page 6-3.

The chip selects are programmed through the use of five 16-bit peripheral registers (Table 5-1). The UMCS Register, offset A0h, is used to program the Upper Memory Chip Select (UCS). The LMCS Register, offset A2h, is used to program the Lower Memory Chip Select (LCS). The Midrange Memory Chip Selects (MCS3–MCS0) are programmed through the use of two registers—the Midrange Memory Chip Select (MMCS) Register, offset A6h and the PCS and MCS Auxiliary (MPCS) Register, offset A8h. In addition to its use in configuring the MCS chip selects, the MPCS Register and the PACS Register are used to program the Peripheral Chip Selects (PCS6–PCS5 and PCS3–PCS0).

Note: The PCS4 chip select is not implemented on the Am186ER and Am188ER microcontrollers.

Table 5-1		Chip Select Register Summary
	Register
Offset	Mnemonic			Register Name				Affected Pins		Comments
A0h	UMCS		Upper Memory Chip Select						Ending address is fixed at FFFFFh
								UCS
A2h	LMCS		Lower Memory Chip Select						Starting address is fixed at 00000h
							LCS
A4h	PACS		Peripheral Chip Select		PCS6–PCS5			Block size is fixed at 256 bytes
					PCS3–PCS0
									Starting address and block size are
A6h	MMCS		Midrange Chip Select		MCS3–MCS0
									programmable
					PCS6–PCS5
									Affects both PCS and MCS
A8h	MPCS		PCS and MCS Auxiliary		PCS3–PCS0
									chip selects
					MCS3–MCS0
ACh	IMCS		Internal Memory Chip Select		None.				See Chapter 6, “Internal Memory.”

Note: A write will enable an external memory or peripheral chip select register.

Chip Select Unit 5-1